1. Field of the Invention
The present disclosure relates to a polarizer and, more particularly, to a coatable polarizer which has a high degree of polarization and transmittance and is low in price and a liquid crystal display having the same.
2. Background of the Invention
In general, a liquid crystal display includes two substrates disposed to face one another at a predetermined space therebetween and a liquid crystal layer injected between the two substrates. Here, liquid crystal has refractive index anisotropy with respect to a shorter axis and a longer axis, making light have a refractive index changing when transmitting through the liquid crystal layer, and a desired image may be realized by adjusting light transmittance.
In order to adjust light transmittance, polarizers are attached to the two substrates. Here, the polarizers are aligned to be parallel or perpendicular to each other in an optical axis direction to adjust transmittance of light incident to or output from a liquid crystal layer, thus realizing an image.
In general, a polarizer is formed by performing coloring based on adsorption of dichroic dye and uniaxial orientation or biaxial orientation on a polyvinylalcohol (PVA)-based resin film, and stacking a transparent resin film, in particular, a polarizer protective film based on an acetic acid cellulose represented by triacetylcellulose (TAC), on one surface or both surfaces of the polarizer on which the dichroic dye has been oriented, through an adhesive layer. The polarizer is bonded to a liquid crystal panel with an adhesive.
However, when the polarizer is manufactured through the related art method as described above, the polarizer becomes relatively thick, leading to shortcomings of poor heat resistance and moisture resistance of the manufactured polarizer, and in particular, since the orientation process (or stretching process) and the dye process are performed on the PVA polarizer, a process time is lengthened and manufacturing cost increases.
In order to solve such problems, a coatable polarizer which is manufactured through a coating scheme has been recently proposed.
Coatable polarizers include a host-guest type polarizer, a lyotropic type polarizer, and the like. In the host-guest polarizer, R, G, and B dyes as guests are mixed to liquid crystal as hosts, and when the hosts are aligned in an alignment direction of an alignment layer therebelow, the R, G, and B dyes are also aligned to absorb light parallel to the alignment direction (absorption direction) of the dyes and allow light perpendicular thereto to be transmitted therethrough, thus polarizing light. In the lyotropic type polarizer, lyotropic polymers are aligned in a row to polarize light. In addition, a wire-grid type polarizer has also been proposed. In the wire-grid type polarizer, metal nanowires are aligned in a predetermined direction on a substrate and a polarization direction of incident light is determined according to an alignment direction of the metal nanowires.
Among the various polarizers, the host-guest type polarizer has been mainly researched in consideration of ease in manufacturing and low manufacturing cost.
However, the host-guest type polarizer has the following problems.
As mentioned above, in the host-guest type polarizer, since the R, G, and B dyes as guests are mixed to liquid crystal as hosts to align liquid crystal, and thus, the R, G, and B dyes are aligned in a particular direction. Here, the dyes, guest materials, cannot absorb every visible light, and thus, three to five types of dyes are mixed to be used to absorb light of a particular polarization component.
However, in the related art polarizer, since the several types of guests are mixed to the host, it is not easy to mix the hosts and the guests in an appropriate ratio, and thus, it is not possible to precisely align the guests along the host. As a solution, the hosts and the guests are mixed in an appropriate ratio to precisely align the guests. In this case, however, since the various types of guests are not sufficiently mixed, a polarization degree is not uniformly maintained in the entire region of visible rays, reducing the polarization degree.